coir facts article

7/30/2019 Coir Facts Article

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Facts on Coir: Lessons f rom the Past( Degradation and strength retention in field applications )

Lanka Santha, P.E.Calista Santha, Ph.D.

RoLanka International, Inc. 1998

Abst ractThere is a rapid growth in the use of bioengineered soil erosion and sedimentation control designsespecially in environmentally sensitive areas. Most of these designs incorporate coir products to providethe required initial structural stability until the establishment of sustainable vegetation. Design criteria inthese designs assume a certain rate of degradation in the coir products. As a result, there is a growingconcern about durability and strength retention in field applications of coir erosion control products. Thisarticle discusses the contributing factors for strength retention and durability of coir products in fieldapplications and several relevant experiences in the use of coir products by horticultural and agriculturalindustries that are applicable to environmentally sensitive soil erosion and sedimentation control designs.

Introduction

Coir (coconut fiber) usage has become very common among professionals in various industries due to itsversatility. In the horticultural industry, agricultural industry, or erosion control industry, coir hasestablished a remarkable reputation for its superiority to other available natural materials. Compared tothe horticultural and agricultural industries, coir is relatively new to the erosion control industry and it maytake some time for this industry to learn and understand about coir. Recognition of coir in the erosioncontrol industry has come from the fact that it is an abundant, renewable natural resource with anextremely low decomposition rate and a high strength compared to other natural fibers. In traditionalerosion control blanket applications, coir blankets are well known for superior performance compared toother organic blankets. In most of these applications, long-term tensile strength in the blankets is not acritical design criterion. The rapid growth of environmentally concerned designers with their innovativebioengineering designs has increased coir use in the erosion control industry. These designs incorporatecoir products as structural components in the construction. Figure 1 shows such a design using high

strength brown bristle coir woven blanket. This design was selected for the Environmental ExcellenceDesign Award at the 1996 International Erosion Control Association (IECA) annual meeting. This awardwinning design expects the woven coir blanket to retain considerable tensile strength until theestablishment of well grown vegetation. Figure 2 is another bioengineering design using coir rolls withhigh strength brown bristle coir outer netting. This design requires the outer netting in coir rolls to retainstrength for several years. Therefore, high strength retention or slow rate of degradation of coir productsin field applications fulfills the design expectations in these types of bioengineering designs.

It is normal for designers to look for more information relative to their design criteria. Because of thisneed, there is a growing concern regarding durability and strength retention in field applications of coirerosion control products. The intent of this article is to discuss the contributing factors for strengthretention and durability of coir in field applications and to present several relevant experiences in the useof coir products by horticultural and agricultural industries that are applicable to erosion control designs.Coir is typically processed from ripe coconut husks which are dark brown in color and have been retted infreshwater for three to six months. The retting process of coconut husks acts as a curing process for fiberin coconut husks. Curing coconut husks in freshwater increases resistance to UV (ultraviolet) degradationand also increases the flexibility of processed fiber without causing deterioration. During traditionalprocessing, coconut fiber from cured husks is separated by skilled labor into grades depending on thelength of fiber. The longer and stronger fibers are called bristle coir and the shorter and thinner fibers arecalled mattress coir (Santha, 1994). Coir processed from ripe husks cured in freshwater is dark brown incolor.


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Figure 1: Bioengineered ri ver bank s tabilization, an innovative fabric-encapsulated technique.

Figure 2: Use of coir rolls in shoreline stabilization.When the ripe coconut husk is dry, it is an excellent firewood. As a result in countries with a highpopulation density, most of the ripe brown coconut husks are used for firewood and the coconut husksavailable for processing coir are unripe green husks. Unripe green coconut husks are usually soaked inbrine to make the coir processing easier (Meerow, 1997). An economical way to soak coconut husks inbrine is to use lagoons (Nedia Enterprises, 1996). Coir processed from lagoon-cured green husks is lightbrown or white in color. This coir is referred to as white coir. Salt in lagoon water makes it easier toprocess unripe green coconut husks. Needless to say, fibers in coir processed from unripe green coconuthusks are not fully mature compared to fibers coming from ripe brown coconut husks. Lagoon-curedbrown coconut husks also produce white coir. Salt in lagoon water acts as a bleaching agent that can

weaken coir used in field applications. White coir is, therefore, much weaker than brown bristle coirprocessed from ripe brown husks.High demand for coir has led to new coir processing methods which may produce a weaker product thanthe traditional freshwater-curing process. Mass-scale coir manufacturers recently implemented coconuthusk defibering machines. These machines can separate fiber from uncured or partially-cured husks orunripe green husks or ripe brown husks. Advantages of these defibering machines to the coir producerinclude reduced expense and faster production rates since skilled labor is not required and the six-monthcuring time is reduced or eliminated. Some of these mass-scale coir manufacturers go further and soakunripe green husks in a bacterial solution and process for white coir within 72 hours of curing (Joseph


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and Sarma, 1997). These machines do not separate fiber into bristle coir and mattress coir but yield amixture of long and short (strong and weak) fibers. A quick way to produce white colored coir fordecorative coir products is chemical bleaching of the coir. In chemical bleaching, brown or light-browncolored coir is treated with chemicals to remove the brown color. Chemical bleaching may have somenegative effects on the strength and durability of coir. On the other hand, coir from the ripe husk is wellknown as a natural fiber and the rich brown color is more attractive than a white color for erosion controlapplications. Most importantly, addition of chemicals to natural coir may create a potentially hazardoussituation in many environmentally sensitive applications.Experience with coir in the agricultural industry has shown that only the traditional brown bristle coir whichis processed from ripe brown coconut husks cured for at least six months in freshwater has performedwell in applications where durability and strength retention are critical for satisfactory field performances.

Experience in the Agricultu ral IndustryFor well over twenty years, hop growers in the agricultural industry have used coir twine to train hop vines(Figure 3). Hop growing season starts in April and harvesting is done in mid-August to September. Asshown in Figure 3, young hop plants climb and grow on the 20 feet long coir twine. When hop vines reachtheir maturity, the vines are very heavy and the twines must be able to carry the weight in wet and windyconditions in hop growing areas (Oregon, Washington and Idaho states). Years ago, hop growers went

through the phase that erosion control industry professionals are now going through, seeking answers toquestions on strength retention and durability of coir in field applications. Coir twines made of differentcoir types were introduced to hop growers by different sources. Finally after years of experience with coirtwines made of different coir types, hop growers determined the only acceptable coir twine for the hopindustry is the 80-90 lb. initial strength brown bristle coir (freshwater-cured) twines. This twine has proventhat it can support hop vines throughout their growing season without any problem. During the period thathop growers used a variety of coir twines made of different coir types, including white coir, they paid ahuge price as coir twines other than the traditional brown bristle coir twines failed to support mature hopvines.

Figure 3: Use of coir twine in hop farms to train hop vines.

Experience in the Horticultural IndustryCoir dust or pith, the leftover dust after extracting coir from coconut husks, was introduced to thehorticultural industry about fifteen years ago as a soilless plant growth medium. Due to its high waterholding capacity and the ability to wet easily without wetting agents, coir dust became more popular thanpeat moss. This popularity has created a high demand for coir dust. Similar to the hop industry, thehorticultural industry found there were different coir dust sources and very soon understood that all


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sources of coir dust do not have similar properties but depend on the processing method. The mainproblem experienced was the high salt content in some coir dust (Cresswell, 1992). The curing ofcoconut husks in lagoons increased the salt content in coir dust. Now there are very strict quality controlpractices for coir dust and some veteran coir dust users go one step further and buy coir dust produced ingeographic regions where saltwater-curing of coconut husk is not available.

An Explanation for Strength Retent ion and Durabil ity of Coir in Field Applicat ionsExperience in the hop industry provides a good example to help us understand coirs strength retentionand durability properties in field applications. Currently, the hop industry uses only the freshwater-curedbrown bristle coir twines. Lets take a closer look at why they chose this after years of trial and error withcoir produced from different methods. Figures 4 shows enlarged cross sections of currently availabledifferent types of coir twines. Figure 4a is an enlarged cross section of freshwater-cured brown bristle coirtwine. Figure 4b is an enlarged cross section of saltwater-cured (lagoon-cured) white bristle coir twine.Figure 4c is an enlarged cross section of freshwater-cured mixed brown coir twine, and Figure 4d is anenlarged cross section of saltwater-cured mixed white coir twine. In general, strength and especially inwet strength, bristle coir twine is stronger than coir twine of similar size made of mixed coir. However, forthe sake of argument, let us assume that all four coir twines shown in Figure 5 have the same initial wetstrength. Conditions to which coir twines are subjected in the hop fields are similar to the conditions coirproducts undergo in erosion control field applications. In both cases, coir is undergoing degradation,

ultraviolet (UV) and biological, while under stress. The higher the resistance to degradation, a product willhave longer strength retention. Lagoon-cured coir contains salts and when it comes in contact withmoisture, degradation is greatly accelerated. As a result, degradation of lagoon-cured coir is much fasterthan freshwater-cured coir. Furthermore, degradation of smaller diameter fibers occurs much faster thandegradation of larger diameter fibers. Increased degradation speed occurs because coir twine made ofsmaller diameter fibers has a significantly higher surface area compared to the same sized coir twinemade of larger diameter fibers. In addition, fibers in white coir processed from unripe green husk areweaker compared to fibers from ripe brown husks. Also, resistance to UV degradation in brown coirprocessed from ripe husk is much higher than white coir processed from unripe green husk. Therefore,coir twine made of freshwater-cured mixed brown coir, lagoon-cured mixed white coir, or lagoon-curedbristle coir has a faster degradation rate than coir twine made of freshwater-cured brown bristle coir(Figure 4a). The same arguments are true for coir twines made of chemically bleached white coir. Thisexplains why freshwater-cured brown bristle coir twines are the most durable and retain the highest

strength in field applications compared to coir twines made of any other coir. The hop industry providesconvincing proof for this explanation showing that freshwater-cured brown bristle coir has superiorresistance to degradation and the highest strength retention compared to any other coir type in fieldapplications. In addition, freshwater-cured brown coir contains no excess salt or chemicals which may bepresent in lagoon-cured or chemically-bleached white coir. Considering horticultural industrys experiencewith coir dust, designers may find it valuable to look closely at the use of coir that has excess salt orchemicals for soil erosion control and bioengineering applications.


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ConclusionsThe most common question today in erosion control and soil bioengineering designs regarding coirproduct usage involves the rate of degradation and strength retention of coir products in field applications.

This issue is basic to total quality control where high quality raw materials and production standards buildhigh quality into the final product. It is time for erosion control industry professionals to look into thefindings of other industries such as horticulture and agriculture for their valuable experience with coir.Such experience will guide the erosion control industry in making better use of coir products and also willhelp to identify problems and failures in coir products without blaming the entire coir industry. It is alsoprofitable for industry professionals to learn the real facts about coir instead of accepting unfounded oruntrue information published solely for purposes of marketing coir products. Most importantly,understanding the contributing factors to coir durability and degradation will help to develop industrystandards for high quality coir products. In todays environmentally sensitive soil erosion andsedimentation control designs where a slow rate of decomposition and a high retention of strength isimportant in field applications, it is wise for designers to look for the brown bristle coir raw material in coirproducts.

References1. Calista R. Santha, Ph.D., "Coir an Abundant Natural Fiber Resources", Land and

Water Magazine May/J une 1994, p 42 - p 43.2. Alan W. Meerow, Ph.D., "Coir Dust, A Viable Alternative to Peat Moss", Internethttp://www.ftld.ufl.edu/coir%20potential.htm.3. Nedia Enterprises, "Product Literature", 1996.4. K. GeorBge J oseph and U. S. Sarma, "Retted (White) Coir Fibre Netting - The IdealChoice as Geotextiles for Soil Erosion Control", IECA Proceedings 1997, p 67 - p 75.5. C. Geoffrey Cresswell, Ph.D., "A Comparison of the Chemical and Physical Propertiesof Coir Dust with Sphagnum and Sedge Peats: Laboratory and Glasshouse Studies",Biological and Chemical Research Institute, Australia.

This article was (Facts on Coir) published in February 1999 Landscape Architect and SpecifierNews magazine was developed from thi s technical paper.

coir facts article

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